b-Mannosidase

PRINCIPLE OF METHOD: Hydrolysis of the synthetic substrate 4-methylumbelliferyl-b-D-mannopyranoside at acid pH is followed by measuring the fluorescence of the liberated 4-methylumbelliferone after stopping the reaction with alkaline buffer.

USES AND LIMITATIONS OF THE METHOD: Deficiency of b– mannosidase is the primary defect in b-mannosidosis, a disorder of oligosaccharide catabolism in which there is increased storage and urinary excretion of the disaccharide Man(b-1->4)GlcNAc. The laboratory screens for the disorder as part of its white cell screen using plasma or serum; any low values are followed up using white cells or cultured fibroblasts. The above mentioned disaccharide is excreted in urine and should be detectable by a TLC screen, but the laboratory does not have experience of diagnosing an affected patient by this method. Prenatal diagnosis should be possible by analysis of chorionic villi or cultured amniotic cells.